1. Field of the Invention
The present invention relates to a rotational micro mirror and, more particularly, to a micro mirror used for scanning a laser beam in a display device such as a laser TV, and a method of manufacturing the same.
2. Description of the Related Art
With the advances of the multimedia era, large screen displays are increasingly demanded, and accordingly, various kinds of large screen display devices have been developed. A laser TV has been suggested as a next-generation display device because of inexpensive manufacturing costs and the possibility of manufacturing it with a large screen that displays high resolution images.
The laser TV includes a light scanner which scans horizontally and vertically laser beams radiating from laser diode modules according to red-green-blue (RGB) image signals. A micro mirror manufactured using a micro-electro mechanical system (MEMS) is used for the light scanner.
FIGS. 1A and 1B are plan views of conventional micro mirrors. FIG. 2 illustrates the operation of the micro mirrors of FIGS. 1A and 1B.
Referring to FIGS. 1A and 1B, the micro mirror includes a rotatable mirror unit 1, a pair of spring units 2 and 2′ connected to opposite ends of the mirror unit 1 to support the mirror unit 1 and act as a rotation axis when the mirror unit 1 rotates, and moving combs 3 and static combs 4 forming a driving unit which rotates the mirror unit 1.
The moving combs 3 and static combs 4 respectively include a plurality of comb-fingers. The moving combs 3 may be installed in the mirror unit 1 as illustrated in FIG. 1A or in spring units 2 and 2′ as illustrated in FIG. 1B. In addition, the static combs 4 are installed in a lower portion or an upper portion of the moving combs 3 as illustrated in FIG. 2 and the comb-fingers of the static combs 4 are arranged to respectively alternate with the comb-fingers of the moving combs 3.
As illustrated in FIG. 2, when first and second comb-fingers 3a and 3b of the moving combs 3 are negatively charged (−), and first comb-fingers 4a of the static combs 4 are positively charged (+), an electrostatic force is generated between the first comb-fingers 3a of the moving combs 3 and the first comb-fingers 4a of the static combs 4, and thus the mirror unit 1 is rotationally driven, as shown with the dotted line in FIG. 2, around a spring unit 2. When second comb-fingers 4b of the static combs 4 are positively charged (+), the mirror unit 1 is rotationally driven in the opposite direction. Due to the rotational driving of the mirror unit 1, incident light is continuously and uniformly reflected in a predetermined range to scan a scanning surface.
A driving speed of a micro mirror is related to the resolution of a display device, and a driving angle is related to a screen size. That is, as the driving speed of a micro mirror increases, the resolution becomes high. As the driving angle increases, the screen size increases. Accordingly, a laser TV with a large screen and high resolution should have a light scanner, that is, a micro mirror, which is rapidly driven and has a large driving angle.
The driving speed of the micro mirror is inversely proportional to the driving angle, and thus it is difficult to obtain both a rapid driving speed of the micro mirror and a large driving angle. Meanwhile, to increase the driving speed of the micro mirror, resonant driving can be used. However, it is difficult to match the inherent frequency of the micro mirror to the driving frequency due to manufacturing errors, and thus manufacturing yield of the micro mirror is low. In addition, an additional tuning structure for adjusting the frequency may be required.
The micro mirror of FIG. 1A has moving combs 3 on sides of the mirror unit 1. In this structure, the distance D1 from a rotation center of the mirror unit 1 is large, and thus the magnitude of a rotational moment is large compared with the micro mirror of FIG. 1B when the same number of the moving combs 3 is used. However, the number of the moving combs 3 is limited. In addition, when a large number of the moving combs 3 is formed, the size of the mirror unit 1 increases, thereby increasing the moment of inertia and decreasing the inherent frequency of the micro mirror, and thus, a rapid driving speed cannot be obtained.
The micro mirror of FIG. 1B has the moving combs 3 formed along spring units 2 and 2′. In this structure, the number of the moving combs 3 can be increased, thereby decreasing the magnitude of moment of inertia, compared with the structure of FIG. 1A. However, the distance D2 from the center axis is short so that a small moment is generated, and thus a sufficient driving angle is not obtained. In addition, elastic coefficients of the spring units 2 and 2′ may not be the same due to a processing error.
Since the conventional micro mirror does not have both a rapid driving speed and a large driving angle, it is not suitable for use in a light scanner for a laser TV having a large size and high resolution.